#include<iostream>
#include<vector>
#include<queue>
#include<cstring>
#include<cmath>
#include<map>
#include<set>
#include<cstdio>
#include<algorithm>
#define debug(a) cout<<#a<<"="<<a<<endl;
using namespace std;
const int maxn=200;
typedef long long LL;
inline LL read(){LL x=0,f=1;char ch=getchar();	while (!isdigit(ch)){if (ch=='-') f=-1;ch=getchar();}while (isdigit(ch)){x=x*10+ch-48;ch=getchar();}
return x*f;}
LL a[maxn];
int main(void){
   	cin.tie(0);std::ios::sync_with_stdio(false);
    LL t;cin>>t;
    while(t--){
        LL n,k;cin>>n>>k;
        a[0]=-1;
        for(int i=1;i<=n;i++) cin>>a[i];
        LL cnt=0;
        for(int i=1;i<=n;i++) if(a[i]!=a[i-1]) cnt++;
        if(k>=1&&cnt==1){
            cout<<"1"<<endl;
        }
        else if(k>1){
            cout<<1+( (cnt-k)+(k-2) )/(k-1)<<endl;
        }
        else{
            cout<<"-1"<<endl;
        }
    }
   	return 0;
}
